The standards for wireless local area network (WLAN) technologies are established by the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards committee. IEEE 802.11a and IEEE 802.11b respectively provide data rates of 54 Mbps and 11 Mbps using unlicensed bands of 2.4 GHz and 5 GHz. IEEE 802.11g adopts Orthogonal Frequency Divisional Multiplexing (OFDM) at 2.4 GHz and provides a data rate of 54 Mbps. IEEE 802.11n adopts Multiple Input Multiple Output (MIMO)-OFDM and provides a data rate of 300 Mbps for four spatial streams. IEEE 802.11n supports a channel bandwidth up to 40 MHz and provides a data rate of 600 Mbps.
The IEEE 802/11af standard for defining operations of unlicensed devices in the TV white space (TVWS) band is currently under development.
TVWS includes very high frequency (VHF) bands (54 to 60, 76 to 88, and 174 to 216 MHz) and an ultra high frequency (UHF) band (470 to 698 MHz) allocated for TV broadcast, and refers to a frequency band allowed to be used by unlicensed devices on condition that they do not disturb communication of licensed devices (devices for TV broadcast, wireless microphones, etc.) operating in the corresponding frequency band.
Although operations of all unlicensed devices are allowed in the range of 512 to 608 MHz and 614 to 698 MHz except for some special cases, 54 to 60 MHz, 76 to 88 MHz, 174 to 216 MHz, and 470 to 512 MHz are allowed for communication between fixed devices only. A fixed device refers to a device performing transmission at a fixed location only. In the following description, a white space band includes the above-described TVWS, but is not limited thereto.
An unlicensed device which desires to use a white space band should provide a function of protecting licensed devices. Accordingly, whether a licensed device occupies a white space band needs to be checked before starting transmission in the corresponding band. That is, the unlicensed device may be allowed to use the white space band only when the licensed device does not use the white space band.
To this end, the unlicensed device should access a geo-location database (GDB) through the Internet or a dedicated network to acquire information about a list of channels available in a corresponding area. The GDB stores and manages information about licensed devices registered therein and information about channels dynamically changed according to geographical locations of the licensed devices and time for which the licensed devices are used. To solve a problem of coexistence of unlicensed devices using the white space, a signaling protocol such as a common beacon frame and a spectrum sensing mechanism may be used.
In the IEEE 802.11 system, a TVWS device may refer to an unlicensed device operating in a TVWS spectrum using an IEEE 802.11 medium access control (MAC) layer and a physical (PHY) layer. In this specification, unless otherwise mentioned, a station (STA) refers to a TVWS device operating in a TVWS spectrum.
STA should provide a function of protecting an incumbent user or a primary user having access priority and including a licensed user (TV user, wireless microphone, etc.). That is, when an incumbent user is using TVWS, STA should stop using a corresponding channel. Accordingly, STA should detect an available channel that may be used by an unlicensed device (i.e., a channel not used by a licensed device) and operate in the available channel.
STA may detect an available channel by performing a spectrum sensing mechanism or by accessing a GDB to find out a TV channel schedule. Energy detection (a scheme for determining that an incumbent user is in use if the intensity of a received signal is equal to or higher than a certain value), feature detection (a scheme for determining that an incumbent user is in use if a digital TV preamble is detected), etc. may be used as the spectrum sensing mechanism. Then, the STA should access the GDB to acquire GDB information based on location information thereof to check whether a licensed device uses a channel in the location. GDB access and information acquisition should be performed a sufficient number of times to protect the licensed device.
Upon determining that an incumbent user is using a channel immediately next to a currently used channel through the spectrum sensing mechanism or GDB, a terminal (or STA) and a base station (or access point (AP)) may protect the incumbent user by reducing transmit power.